Although red blood cell transfusions can be lifesaving, they are not without risk. In critically ill patients, red blood cell transfusions are associated with increased morbidity and mortality, which may increase with prolonged red blood cell storage before transfusion.
Recent studies support a growing appreciation that hemolysis represents one fundamental mechanism associated with increased mortality and morbidity after receipt of red blood cell transfusions.
This concept evolved from clinical trial observations suggesting that trauma patients receiving hemoglobin-based oxygen carriers developed hypertension and multi-organ injury caused by hemoglobin-NO-scavenging-reactions, and clinical observations of vasculopathy complications in patients with hemoglobinopathies and hemolytic anaemia.
Hemolysis represents a problem encountered with red blood cell transfusions, in particular upon prolonged storage prior to use. Hemolysis results in the release of free hemoglobin (fHb). fHb is a source of heme, which in turn can contribute to increased damage caused by reactive oxygen species.
Aerobic organisms are well endowed with enzymatic oxidant defence systems, which provide protection against activated oxygen species. However, damages caused by reactive oxygen can be greatly amplified by redox-active iron. One abundant source of potentially toxic redox-active iron is heme, and both exogenous and endogenous heme can synergistically enhance oxidant mediated cellular damage.
Heme is quite hydrophobic, readily enters cell membranes, and greatly increases cellular susceptibility to oxidant-mediated killing. Heme also acts as a catalyst for the oxidation of low-density lipoprotein (LDL), generating products toxic to endothelia.
The toxic effects of heme may be important in a number of pathologies. These include not only acute conditions such as intravascular hemolysis (which can lead to renal failure) but also more insidious processes such as atherogenesis, in which intra-lesional deposits of iron (perhaps derived from erythrocytes, which are known to intrude into atherosclerotic lesions) have been observed.
Free hemoglobin in plasma, when oxidized, can provide heme to endothelia, which greatly enhances cellular susceptibility to oxidant-mediated cell injury.
A second factor contributing to adverse effects observed in relation with red blood cell transfusions are so called microvesicles (MV). MV, also described as ectosomes, are populations of phospholipid vesicles of 1 μm or less, released into the blood by erythrocytes, platelets, white blood cells or endothelial cells. The production of MV is a highly controlled process, triggered by various stimuli, including cell stimulation and apoptosis. If MV have been first described as cell dusts, they are now recognized as being involved in a broad spectrum of biological activities, such as thrombosis and hemostasis, inflammation, vascular and immune function, apoptosis or even intercellular communication by the transfer of surface proteins.
While MV also can be detected in healthy individuals, their increase has been observed in a variety of diseases with elevated thrombotic risk, vascular involvement or metastasis.
Typically, blood products such as blood or blood components (e.g. red blood cells, platelets, plasma) undergo further treatment and storage prior to their administration to a subject in need thereof. It has been known that the quality of blood or blood components may decrease with increased storage times. In particular, the concentration of fHb and MV in the blood product increases with increasing storage time.
In particular, under blood bank conditions, red blood cells undergo progressive structural and biochemical changes commonly referred to as “the storage lesion”. Red blood cells (also designated as erythrocytes) show progressive cell shape transformation from biconcave disk to rigid sphero-echinocyte, accompanied by the release of MV from the tips of spicules and their accumulation in the blood product. In addition, there is a depletion of ATP, pH acidification, and hemolysis, the hemolysis resulting in the accumulation of fHb.
Red blood cell membrane modification during storage is triggered by ATP depletion and oxidation and is centred on changes in band 3, leading to membrane detachment and disorganization that probably affect red blood cell deformability, osmotic resistance and survival after transfusion.
Red blood cell MV formation represents a continuous process of membrane remodelling, which occurs early during blood banking, and prevents the exposure of phosphatidylserine on red blood cells. MV found in red blood cell concentrates generally originate from red blood cells and their number gradually increases with storage time.
However, there is an increasing demand for blood products, while the blood supply by donors is fluctuating, resulting in the periodical shortage of blood products. Thus, improving the quality and safety of stored blood products is important to address the increasing demand.
Therefore, it is highly desirable to reduce the content of fHb and MY in blood products such as whole blood or blood components, in particular those comprising red blood cells, prior to their administration to a subject in need thereof. This would improve safety and quality of the blood product, also after prolonged storage times.
Attempts have been made to “wash” blood or blood components, in particular those comprising red blood cells, after storage and prior to administration, in order to remove cellular debris and undesired substances from the stored blood product. To that end, attempts have been made to resuspend red blood cells in saline, followed by centrifugation and separation from the supernatant. However, this method is very time consuming and expensive, because it must be performed under sterile conditions in order to avoid the risk of infection for the recipient.
On the other hand, methods aiming to slow down the development of storage lesions (e.g. by storage of red blood cell containing blood products under anaerobic conditions) require the treatment of all blood products already after blood collection and therefore, prior to storage of the product. Thus, this approach does not allow selective treatment of only those blood products requiring said treatment due to prolonged storage. Instead, all blood products are treated, irrespective of storage time. This again results in increased cost and may also result in prolonged handling times.
Thus, there is a need for methods and devices for improving the quality and safety of stored blood products, in particular products comprising red blood cells, prior to their administration to a subject in need thereof.